1. Field of the Invention
This invention relates to a phase change optical recording medium, a method for recording such medium, and a apparatus for recording such medium.
2. Prior Art
Highlight is recently focused on optical recording media capable of recording information at a high density and erasing the recorded information for overwriting. One typical overwritable optical recording medium is phase change optical recording medium which is used by irradiating the recording layer with a laser beam to change its crystalline state whereupon a change in reflectivity caused by the change of the crystalline state is detected for reading of the information. The phase change optical recording media are of great interest since the optical system of the drive unit is simple as compared to magnetooptical recording media.
The recording layer of phase change type is most often constituted from a material of chalcogenide system such as Gexe2x80x94Sbxe2x80x94Te system which provides a substantial difference in reflectivity between the crystalline and the amorphous states as well as a relatively stable amorphous state.
When information is recorded on the optical recording medium of phase change type, a laser beam of high power (recording power) is applied so that the recording layer is heated to a temperature higher than the melting point. In the region where the recording power is applied, the recording layer is melted and thereafter quenched to form an amorphous record mark. When the record mark is erased, a laser beam of relatively low power (erasing power) is applied so that the recording layer is heated to a temperature higher than the crystallization temperature and lower than the melting temperature. The record mark to which the laser beam of erasing power is applied is heated to a temperature higher than the crystallization temperature and then allowed to slowly cool to recover the crystalline state. Accordingly, in the optical recording media of phase change type, the medium can be overwritten by modulating the intensity of a single light beam. However, when a medium wherein the medium structure and the composition of the recording layer are optimized for use at a particular linear velocity is overwritten at a linear velocity higher than the designed linear velocity, the record marks formed can be no longer crystallized by the same erasing power, and in other words, the record marks become unerasable.
The object in the invention described in JP-A 11380/2000 is speeding up of the recording, and in particular, speeding up of the formatting of a phase change optical recording medium. In the recording of the data in an overwritable phase change optical recording medium in the invention described in JP-A 11380/2000, a higher linear velocity is used for the initial recording operation wherein the data are recorded in the unrecorded area for the first time compared to the overwriting operation wherein the data are overwritten. JP-A 11380/2000 states that the entire surface of the phase change optical recording medium is initialized (crystallized) after its production no erasure is required in the formatting, and as a consequence, no problem is associated with the recording at a linear velocity higher than the one used in the overwriting operation. JP-A 11380/2000 also states that the formatting can be accomplished by the recording at binary values, namely, at the recording power and the reading power since the formatting does not require the erasure.
The inventors of the present invention have conducted an experiment wherein the initial recording to the unrecorded area is conducted at a linear velocity higher than the optimal linear velocity employed in the overwriting operation as in the case of the invention described in the JP-A 11380/2000. It was then found that increase in the jitter is induced in both cases wherein no erasing power is applied and wherein normal erasing power (the erasing power used in the overwriting operation) is applied in the initial recording to the unrecorded area.
An object of the present invention is to reduce the time required for the recording of the unrecorded area in the recording of the recording layer of the phase change optical recording medium. Another object of the invention is to reduce the jitter produced in such recording.
Such objects are attained by the present invention of the constitution as described in any of the (1) to (11), below.
(1) An optical recording method for recording an optical recording medium having a phase change recording layer wherein the recording is conducted such that:
Vw/Vo greater than 1,
and
0.3 less than Pew/Peo less than 1
when the unrecorded area of the recording layer is recorded by using a linear velocity of Vw and an erasing power of Pew and overwritten by using a linear velocity of Vo and an erasing power of Peo.
(2) An optical recording method according to the above (1) wherein the recording is conducted such that:
2xe2x89xa6Vw/Voxe2x89xa620.
(3) An optical recording method according to the above (1) or (2) wherein the recording is conducted such that:
0.5xe2x89xa6Pew/Peoxe2x89xa60.9.
(4) An optical recording method according to any one of the above (1) to (3) wherein the recording is conducted such that:
Pww/Pwo greater than 1
when the unrecorded area of the recording layer is recorded by using a recording power of Pww and overwritten by using a recording power of Pwo.
(5) An optical recording method according to the above (4) wherein the recording is conducted such that:
1.1xe2x89xa6Pww/Pwoxe2x89xa62.
(6) An optical recording method according to any one of the above (1) to (5) wherein said method is conducted by using an optical recording medium having recording conditions used in the overwriting operation and recording conditions used in the recording of the unrecorded area.
(7) An optical recording method according to any one of the above (1) to (6) wherein said unrecorded area is either an area which has never been recorded after the initialization or an area which has been erased after recording.
(8) An optical recording method according to any one of the above (1) to (7) wherein said linear velocity Vo is the optimal linear velocity in the overwriting operation and said Peo is the optimal erasing power in the overwriting operation.
(9) An optical recording method according to any one of the above (1) to (8) wherein said medium is not overwritable at said linear velocity Vw.
(10) An optical recording apparatus for conducting the optical recording method according to any one of the above (1) to (9).
(11) An optical recording medium to which the optical recording method according to any one of the above (1) to (9) is applied, wherein said medium has recording conditions used in the overwriting operation and recording conditions used in the recording of the unrecorded area.